Transducer-controlled servomechanism



3 Sheets-Sheet 1 REG jab

R. C. BENTON TRAN SDUC ER-CONTROLLED SERVO- MECHANISM INPUT POWER MODULATOR AMPLIFIER Aug. 21, 1962 Filed April 4. 1960 MA/I,

OSCILLATOR v! 0 mm w mm m W n m6 A m w w P.

30500 OR w 31/ 1962 R. c. BENTON 3,050,034

TRANSDUCER-CONTROLLED SERVO-MECHANISM Filed April 4, 1960 3 Sheets-Sheet 2 INVENTOR. Robert 6 Benton Aug. 21, 1962 R. c. BENTON 3,050,034

TRANSDUCER-CONTROLLED SERVO-MECHANISM Filed April 4, 1960 FLOW RATE NON- TURBULENCE:

CA VIIATIONAL TURBULENT 4 CAVITATION 3 Sheets-Sheet 5 be C. Benfon 8L BY WM Fig. I'QM' HIS1d sfl 3,050,034 Patented Aug. 21, 1962 3,050,034 TRANSDUCER-CGNTRGLLED SERVO- MECHANISM Robert C. Benton, State College, Pa, assignor to Centre Circuits, Inc, Pine Grove Mills, Pa., a corporation of Pennsylvania Filed Apr. 4, 1960, Ser. No. 19,751 18 Claims. (Cl. 121-38) is invention relates to transducer'controlled servomechanism, and particularly a servo-mechanism of the hydraulic type. It conforms to a so-called open valve system of operation so as to produce exceedingly high frequency action of response.

The principle of control in the invention resides in a transducer element arranged, when in contact with a flowing stream, to convert energy input into hydraulic energy directly therein or else doing so indirectly by transforming the energy first into sonic energy which is straightway converted into hydraulic energy. This energy varies impedance in the flow which is materially distributed thereby and the resulting turbulence appreciably changes the pressure drop along the path of the stream and particularly where it encounters a change in cross section in the path such as afforded by a fixed, permanently open restriction. The present application of this principle is believed new, whereby it is the state of the liquid which prevents it from negotiating the change of cross section so readily instead of the converse principle whereby a restriction is throttled or physically closed off in the popular way. In other words, the restriction is substantially the restriction it always was and the impedance is externally created in the flow itself.

The servo-mechanism according to this application is particularly adapted for hydraulically operating a fastacting element such as a valve. More specifically, according to the several embodiments disclosed, it comprises firstly a piston and a cylinder connected to the valve element and having an effective longitudinally acting pressure area acting to move said element; secondly, a passage which is permanently open but restricted, and which is tapped at a point so as to communicate working pressure to the longitudinally acting pressure area; an electrically responsive transducer device connected to that passage for impeding the flow of fluid in the passage at an electrical frequency; and finally, controlled-input, power delivery means for applying power to operate said electrically responsive device for varying the impedance in said fiow whilst the latter continues through said permanently open restriction.

I thus utilize what. in effect, constitutes and is, in fact, called an open-valve system in the analogous arts. Because the fluid therein can accordingly be kept in a constant motion of circulation irrespective of its state, there is little or no inertia problem to overcome in effecting adjustments. The reaction time is infinitesimally low for this reason and for the added reason that where the disturbing electrical frequency in the transducer is 60 kc., for instance, the corresponding time to complete any one cycle of a given amplitude would be 1.7 microseconds; hence, a succession of changed amplitude cycles to which the transducer is shifted can transpire and make its effect be felt quite rapidly. That is to say, one cycle of a disturbing amplitude of another frequency may be insufficient to appreciably change the degree of turbulence in a stream of flow, whereas a succession thereof, even though occurring in an exceedingly short time interval, can cause a material adjustment of flow.

Further features, objects and advantages will either be specifically pointed out or else become apparent when, for a better understanding of the invention, reference is made to the following written description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a partially schematic diagram of a valveoperating servo-mechanism embodying transducer control principles according to the present invention;

FIGURES 2 and 3 are longitudinal and transverse cross-sectional views of one of the transducer control elements of FIGURE 1;

FIGURE 4 is a hydraulic performance curve showing flow through a transducer plotted against its amplitude of vibration;

FIGURE 5 is a modification showing a single acting valve-operating servo-mechanism according to the inven tion;

FIGURES 6 and 7 are further modifications showing different types of static restrictions in the flow path;

FIGURE 8 shows a piezoelectric type of transducer similar to the preceding embodiments but externally positioned;

FIGURE 9 shows a piezoelectric type of transducer which is externally positioned and which is modified to operate on principles of a sonic valve;

FIGURES 10 and 11 are variations differing from one another but in common, they employ a magnetostrictive type of transducer element;

FIGURE 12 is a modification illustrating a single restriction type of piezoelectric transducer control;

FIGURE 13 shows a modification of the servo-mechanism which operates at an electrical frequency but according to a different principle; and

FIGURE 14 is a transverse cross-sectional view taken along the lines XIVXIV of FIGURE 13.

More particularly in FIGURE 1 of the drawings, a servo-mechanism for operating a high-speed hydraulic valve 22 is shown comprising a double acting cylinder 24 in which a piston 26 is slidably mounted and with which the piston defines an effective longitudinally acting pressure area acting to operate the valve. For this purpose, a pump 28 acting through a pressure regulating valve 30 supplies hydraulic fluid through a split path at a pressure P for delivery to the opposite ends of the double acting cylinder 24. Fluid leaves the left end and the right end of the cylinder 24 as viewed in FIGURE 1 at the respective pressures P and P which vary for the reasons hereinafter set forth and passes thence through a pair of oscillating transducer elements whereupon the split paths reunite in a common portion 34 having the common pressure P for recirculation through the pump 28. Pump speed is regulated with the desire to produce active circulation but at rates not appreciably exceeding the point at which natural laminar flow starts to become turbulent.

Two nozzle shaped static restrictions 36 are introduced at upstream points in the split paths and the consequent series of pressure drops in the flow paths results in establishing the relations P P P and P P P The transducer elements32 are illustrated to be of the same size and the upstream restrictions 36 are likewise of the same size so as to equally divide the flow whenever P is equal to P however, it is not essential that the flow rate in the split paths be balanced in this situation.

In operation, whenever a differential of pressure is created across the servopiston 26 such that P P the thrust is resisted by a coil spring 38 which is seated on a closure means 40 at one end of the cylinder 24. The coil spring 38 surrounds a piston rod 42 which extends at that end through the closure means 40 and which carries a snap ring 44 engaged by the spring 38,

The piston rod enters the valve 22 through the usual sealing gland, not shown, and i connected in conventional way through hangers and the like. not shown. to a gate 46 or other control element usual in valve constructions. Due to the pressure differential referred to, the piston moves toward its dotted line showing seeking to establish a newly balanced position with the spring 38 and simultaneously moves the gate 46 to the open position shown in dotted lines. The opposite end of the piston rod 42 moves a proportional amount through an end closure means 48 on the cylinder 24 so as to take the extended position shown by dotted lines. The coil spring 38 can be arranged as a valve opening spring if desired although, as illustrated, it conforms to fail-safe practices so as to operate as a valve-closing spring.

Means for applying power to oscillate the transducers 32 and control the pressures P and P is provided as follows. A modulator 50 couples the output of an adjustable oscillator 52 to a substantially balanced power amplifier 54. The modulator 50 is controlled by hand or, as illustrated, by means of an automatic input device 56 such as a program tape reader. The oscillator 52 is readily adjusted beforehand to oscillate at a fixed frequency equal to the resonant frequency of the transducers 32 which are connected in the output of the power amplifier 54. The modulator 50 is preliminarily adjusted so that anterior pressure P to one of the transducers 32 becomes the higher pressure in the cylinder 24, which can be accomplished by a modulated input to that transducer so that it operates at a slightly higher amplitude of vibration than the other modulated transducer 32 controlling the cylinder pressure P This adjusted differential of pressure acting on the longitudinally acting area of the servo-piston 26 practically counters the thrust of the spring 38 in this so-called balanced position, but not quite.

In operation of the piston of FIGURE 1, the input device 56 is effective to modulate the substantially balanced output from the oscillator 52 unequally, thereby unbalancing the output of the amplifier 54 to cause a differential in the impedance in how as between the split paths communicating with the hydraulic cylinder 24. With each change of input from the device 56, the servopiston 26 rapidly moves seeking a position rebalancing itself against the spring 38. The pressure of the fluid at the pressure P is caused to rise whenever the input to the associated transducer 32 is increased for the reason that the increased amplitude of vibration causes a higher impedance in the flow and hence, a reduction in flow. Thereupon, it can be stated that the reduction in flow which similarly occurs in the associated upstream orifice 36 causes less pressure drop across that orifice than before and hence, the pressure P rises so as more nearly to approach the input pressure P Stated another way, the back pressure builds up anterior to the associated transducer 32 which is downstream thereof, each time the transducers resistance to flow increases. This build-up changes the pressure differential across the piston, thus forcing it in one direction to respond and seek another balanced position, thereby compressing the spring 38 until the thrust of the piston is exactly countered by the spring. When it operates in the other direction, the piston follows the spring allowing the latter to expand until the two forces reach a balance.

The amplitude of thevibrating transducer 32 controlling the pressure P is always electrically decreased at the time at which the amplitude of vibration of the other transducer 32 is increased and vice versa so that their effect is cumulative on the piston 26 to make it respond very rapidly.

In FIGURES 2 and 3, the transducer 32 contained in the downstream passage 58 of either split path comprises a hollow body 60 which consists of a piezoelectric material such as quartz and which, as illustrated, is barium titanate crystal. It is carried in an insulative holder 62 about the outer periphery; the interior periphery forms the restriction in this embodiment and is nozzle-shaped for improved flow characteristics. A layer of foil 64 on the outside and a fired metallic film such as brass 66 on the interior surface form the respective outer and inner electrodes which, when subjected to alternating voltages, make the element 60 change'in physical dimensions and dynamically shrink and enlarge the nozzle once each cycle in imperceptible changes. These voltages are applied through conductors leading from the power amplifier, not shown, and connected to the respective electrode terminals 68 and 70. One of these terminals may be grounded if desired and the terminal 63 connected tothe outer electrode is so indicated. These cross-sectional views utilize solid lines to show the element 60 and the inner electrode 66 at the end of their expanding stroke of oscillation, whereas the outline thereof shown in dotted lines is a greatly exaggerated showing of the same at the end of their contracting stroke of oscillation.

The natural frequency for transducer elements 60 of the type selected is somewhere within either the sonic frequencies whichcan be defined as an audible vibration between 10 cycles per second and 20,000 cycles per secend, or the ultrasonic frequencies which can be roughly defined as from 20,000 cycles per second to 60 megacycles per second or higher. The reason for selecting a crystal element 60 so that its resonant point falls within this desired operating range is that the maximum power input required is of the order of ,3 the power that might otherwise be required to produce a like amplitude of vibration. The size, cut-axis, mass, proportions, and composition of the crystals are selected in accordance with accepted crystal design practices to yield natural frequencies of the general value sought.

FIGURE 4 is a graph of the flow characteristics of a transducer nozzle of the character described in the preceding figures. To determine these characteristics, the transducer is deenergized to the fixed dimension or static state and a specified rate of substantially laminar fluid flow S is introduced therethrough. Thereafter, a rising alternating voltage is applied to the electrodes of the transducer at the natural frequency above specified and the flow rate is measured for each power input at the fixed frequency. For low power inputs, the flow rate as it progresses through the successive values S, L and R marked on the curve is seen to reduce in substantially linear relationhip with increases in the amplitude of vibration. The area under this portion of the curve is crosshatched for ready identification as turbulent but noncavitational flow through the transducer. This area is terminated on the right by a dotted vertical cavitational line which intersects the curve at a point K forming a knee point in the curve.

Under power inputs and vibrational amplitudes corresponding to the knee point K and higher, the flow behavior of the transducer is nonlinear and the curve shows that a considerable and rather drastic reduction in the flow rate occurs in the non-linear portionof the curve. It is to be appreciated that excessive cavitation not only will seriously impede the flow but if sustained, will eventually cause damage and pitting to the interior surface of the inner electrode 66 of the transducer leading to ultimate failure.

In the so-called balanced state of the power amplifier 54 of FIGURE 1, the adjustment thereto by means of the modulator 50 is such as to keep the pressure P the I slightly higher pressure in the cylinder 24 and thus the corresponding operating point R on the curve of FIG- URE 4 will be slightly to the right of the instantaneous operating point L corresponding to the flow rate of the fluid at the pressure P To provide the proper differential for opening the gate 46, the instantaneous operating point R will be caused to shift to the right on the curve of FIGURE 4, whereas the corresponding operating point L at that instant will shift to the left for proportionately reducing the pressure P The converse effect. i.e., where P ZP gives added impetus to the spring 38 in moving the valve gate -16 toward its closed position.

In FIGURE 5 showing a single transducer modifica- 75 tion, the transducer 32 contained in the hydraulic fiow passage 58 is used to control the back pressure on the bottom chamber of a single acting cylinder 124. When the transducer 32 operates to reduce this back pressure, a servo-piston 126 in the cylinder is moved downwardly by a spring 138 to a corresponding point where the extended spring will exactly balance the reduced'pressure. A gate 146 in a valve 122 is connected to the servo-piston 126 so as to open a proportionate amount. With an increase in the amplitude of vibration of the transducer 32, the gate 146 moves to a more-nearly closed position due to the fact that an increase in back pressure results which causes the servo-piston 126 to move compressing the spring 138 and seeking therewith a newly balanced static position.

Though not essential in the embodiment of FIGURE 5, an upstream orifice 36 can be provided in the passage 58 for improved stability of pressure control. The orifice 36 illustrated is nozzle-shaped in the interior so as to be conducive to substantially laminar flow. The use of a single transducer 32 and a single acting cylinder 124 in this embodiment makes it more economical than the structure of FIGURE 1, but the response is somewhat slower.

The modification of FIGURE 6 illustrates an instance where the upstream orifice in the flow passage I58 consists of a thin-edged orifice 135. In this case, the transducer 132 has an interior which is not nozzle-shaped but which takes the form of a thick-edged orifice due to the uniform cylindrical shape of the inner electrode 166. It can be used with single transducer, single-acting cylinder systems, with dual transducer, double-acting cylinder systems, etc.

In FIGURE 7, the restriction 236 inthe hydraulic passage 258 takes the form of a thick-edged orifice or, in other words, an orifice of which the length-to-diameter ratio is unity or greater. The companion transducer 232 does not require any. particular form irrespective of whether the upstream orifice is thin-edged or thick-edged but, as illustrated in FIGURE 7, forms a thick-edged orifice.

In the modified embodiment of FIGURE 8, the transducer 332 has an outer electrode 364 which, except for being ungrounded, is the same as the outer electrode of the preceding embodiments. In contrast to those embodiments, however, the transducer 332 is arranged so that the tubing defining the hydraulic passage 353 forms the inner electrode gripped thereby but this inner electrode does not constitute the restriction. Instead, a static, permanently open, thin-edged orifice 366 fonns the re striction and when alternating voltage is applied to the transducer 332 causing it to vibrate, these vibrations are transmitted by the walls of the passage 358 directly into the passing fluid so as to produce non-cavitationnl turbulence or turbulent cavitation as the need requires. With impedance in the flow itself, the fluid in this state of agitation can resist flowing through the thin-edged orifice 366 to a degree desired. For convenience, the inner electrode is the grounded one so as to enable the passage 358 to be ground potential and thus shock-free to the hand. The orifice 366, which can be nozzle-shaped, a thick-edged orifice or the like, is a thin-edged orifice as actually illustrated and, in any event, its dimensions are fixed.

In the modified case of FIGURE 9, agitation is introduced into the liquid flow at a point upstream of a static, permanently open restriction 466 similarly to the preceding embodiment of FIGURE 8. In this case, however, the barium titanate crystal 432 or suitable piezoelectric body is suspended within one end of a cylinder 434 which is closed at that end by means of a parabolic reflector 436. The crystal 432 oscillates and produces waves due to an alternating voltage which is impressed by an adjustable power oscillator 452. The crystal is so located at the central vicinity of the reflector 436 that the energy waves will reflect and pass through the fluid medium to a focus point 454 which approximately intersects the center line of the passage 458 upstream to the restriction 466. Greater agitation at this point produces commensurately larger impedance in the how which, in turn, increases the resistance of flow through the restrict-ion 466. A diaphragm 460 across the juncture between the cylinder and the passage sealingly separates the fluid within the passage 45% and the fluid within the cylinder 434 and this diaphragm is preferably made of metal such as steel which for all practical purposes is transparent to waves transmitted at the frequencies herein contemplated.

The cylinder 434 is filled with a fluid which is selected so as not only to be a good acoustic conductor but also to afford a good impedance match with the fiuid within the passage 458, thereby providing good efficiency for the transfer of the wave energy. This case is referred to as the sonic valve embodiment due to the fact that the waves advance at the speed of sound through the fluid within the cylinder 434 and in the passage 458.

In the modification of FIGURE 10, a hollow-cored magneto-strictive element constitutes the transducer 532 interposed in the hydraulic fluid passage 558. It is subjected to pulsating flux by means of a concentric surrounding coil 534 which is energized by a variable frequency oscillator 552. The hollow core of the transducer 532, as illustrated, is in the shape of a thick-edged orifice.

The embodiment of FIGURE ll illustrates another magnetostrictive transducer 632 which is likewise surrounded by a pulsating current coil 634 and is separated therefrom by means of the intervening hydraulic passage 658. The resulting pulsating or alternating magnetic field causes the element 632 to elongate and contract longitudinally, its fully contracted stroke of oscillation being shown in solid lines. In the elongating stroke of its oscillation, the element 632 takes the outline shown in somewhat exaggerated fashion by the dotted lines.

It can thus be seen that the fluid adjacent the planes of the opposite end faces of the magnetostrictive element will tend to be agitated so that the upstream portion of the fluid Will resist flowing through the interior of the preceding element 532 and the present element 632. The interior of the body of the element 632 in FIGURE 11 is shown to be nozzle-shaped for improved flow ethciency. A large group of magnetostrictive material is available for these bodies including powder iron-nickel products, ferroceramic products such as ferrox-cube as it is commercially known by its proprietary name, pure nickel, alnifer, and various compositions of ironnickel alloys.

In the modified embodiment of FIGURE 12, the hydraulic passage 758 compared to the tubing of the other embodiments is uniform diameter thin tubing of reduced cross section. There is no restriction as such because the passage 758 itself constitutes the combined upstream restriction, downstream restriction, and inner electrode gripped by the piezoelectric transducer 732 illustrated. Preferably, therefore, the inner electrode is the grounded one as indicated by dotted lines and alternating voltage is applied by appropriately modulated oscillator means, not shown, to the outer electrode 764.

It is immaterial what form of valve is operated by the foregoing embodiments of transducer-controlled servomechanism and is likewise immaterial what form of liquid that the valve is controlling or what form of vapor or gas. So far as the servo-mechanism itself is concerned, water constitutes a satisfactory form of circulating liquid and because it has been observed that the valve ellcct Works better with lower vapor pressure and with lower boiling point liquids, it is desirable if water he used. that it have an additive lowering its vapor pressure and boiling point. Another suitable liquid is alcohol and in general. the lighter weight hydraulic fluids are the ones which are preferred.

In the embodiment of FIGURES l3 and 14, the hydraulic passage 858 has a round cross section with a por tion 858a therein where it widens and at the same time materially flattens in cross section; the poles of a fixed magnet 860 confront the passage portion 858a on its opposite flat sides and a pair of narrow electrode plates S64 and 866 is disposed within the portion 8530 one at each of the narrow ends of its cross section.

If a potential difference exists between the two electrodes 864 and 866 and if aconductive fluid is present therebctween, there are theoretically present small conductive filaments or lines of molecules in the fluid such as indicated by the dotted lines 868 through which current flows from one electrode substantially straight to the other. This condition exists irrespective of whether the potential difference alternates or has the so-called zero electrical frequency characteristic of direct current. In either case, the greater the potential difference, the greater is the resistance to flow of this fluid when it is forced to move through the transverse field created by the poles of the magnet 860.

The output of a power amplifier S70 is applied to the plates S64 and 866 by suitable means and in the AC. version illustrated, a transformer 872 is used for coupling the output to the electrodes so as to produce oscillations in the fluid. As illustrated, an input signal is applied to a modulator 874 so as to modulate the signal of an oscillator 852 being applied to the modulator and supplied therethrough to the power output amplifier 370.

As the output of the amplifier S70 is applied at zero electrical frequency or at some alternating electrical frequency to the electrodes, an increased output creates increased resistance of flow of the conductive fluid and vice versa and, hence, an increasing or decreasing back pressure is available for servo-mechanism purposes. The fluids preferred are mercury, salt water, or other highly conductive liquids, inasmuch as they are the most susceptible under the circumstances to the retarding etfectof a constant magnetic field.

The servo-mechanism according to the foregoing figures of drawing incorporates the transducer element generally in the downstream position relative to the cylinder tap. It is evident that the transducer can be employed to equal advantage at an upstream point so as to control the cylinder tap by starvation instead of as a means of back pressure control. As above indicated, the upstream fixed restriction can be eliminated in many cases where the transducer is used in the downstream position; conversely, when the transducer is used in the upstream position, the fixed orifice can be sometimes omitted or else it is employed in the downstream position relative to the cylinder tap. So also, various figures of the draw mg such as FIGURES 6, 8 and 9 disclose a fixed thinedge orifice employed in the immediate vicinity of or in series with different transducers but self-evidently a thickedged orifice or a nozzle-shaped orifice can be employed in lieu of one another orin lieu of the thin-edged orifice and vice versa. In any case, all static orifices are herein referred to as fixed restrictions to distinguish them from the dynamic ones referred to whose walls vibrate Ol ptherwise physically change in dimensions during operaion.

Variations within the spirit and scope of the invention described are equally comprehended by the foregoing description.

I claim:

1. In servo-mechanism having a movable wall at one side of which is formed a variable pressure working chamber, control structure for developing a back pressure communicated to said chamber including a fluid flow passage presenting permanently open, restriction means in fixed locations or" connection in said structure, and further means connected to said structure including an oscillatory transducer device for changing the resistance of said restriction means to flow by creating varying degrees of turbulence in the stream of fluid passing through said fluid passage thereby varying the buildup and decrease of back pressure in said chamber.

2. In servo-mechanism having a movable wall at one side of which is formed a variable pressure working chamber, control structure for developing a working pressure in said chamber including a circulating fluid system tapped at a point so as to communicate fluid pressure to said chamber, restrictive points in said system formed by permanently open orifices connected respectively upstream and downstream of said tapped point in the system, and further means connected to said structure including an oscillatory transducer device for changing the effective resistance at one of said restrictive points by creating varying degrees of turbulence in the fluid circulating through the associated orifice thereby varying the buildup and decrease of pressure fed to said chamber.

3. In servo-mechanism having a movable wall at one side of which is formed a variable pressure working chamber, control structure for developing a working pressure in said chamber including a circulating fluid system tapped at a point so as to communicate fluid pressure to said chamber, a permanently open orifice forming a restrictive point arranged in said system so as to be in series with the tapped point in said system, and means for imperceptibly changing the physical dimensions of said orifice at electrical frequencies so as to physically disturb the immediate film of fluid in contact therewith.

4. In servo-mechanism having a movable wall at one side of which is formed a variable pressure working chamber, control structure for developing a working pressure in said chamber including a circulating fluid system tapped at a point so as to communicate fluid pressure to said chamber, a permanently open orifice forming a fixed dimension restriction arranged in said system at a point.

in series with said tapped point in said system, and means for impeding flow through said fixed dimension restriction by introducing turbulence in the stream of said circulating fluid at a point therein before it leaves said restriction.

5. Means for hydraulically operating a fast-acting element comprising, in combination, a piston and a cylinder connected to said elementand having an effective longitudinally acting pressure area acting to move said element, a passage which changes in cross section at a first point but is permanently open, and which is tapped at a point so as to communicate working pressure to said pressure area, an electrically responsive device connected to said passage for impeding the flow of fluid in said passage at said first point at an electrical frequency, and controlledinput, power delivery means for applying power to operate said electrically responsive device for varying the ,im-

pedance in said flow whilst the latter continues through said permanently open passage.

6. In servo-mechanism having a movable wall at one side of which is formed a variable pressure working chamber, fluid stream control structure for developing a back pressure communicated to said chamber including a fluid flow passage presenting permanently open restriction means in fixed connection within said structure, an oscillation producing circuit, and transducer means operated substantially at resonance by said oscillation producing circuit and connected to the fluid in said structure for controlling the fluid stream. whereby the resistance of said rcstriction means to the stream and the back pressure in said chamber varies in dependence on the turbulence created by the transducer means in the stream of fluid passing through said fluid passage.

7. In apparatus of the character described, the combination of a split-path hydraulic system, and electrical means including a pair of electrically responsive devices each connected to a different one of said paths for impeding the flow of hydraulic fluid in said path at an electrical frequency, said electrical means further including an oscillator. a substantially balanced amplifier, the output of which is generally equally supplied to the electrically responsive devices to create balanced impedances in the flow through said split paths, and adjustable means coupling the output of the oscillator to the amplifier and adjustable to modulate said output unequally for thereby unbalancing the output of said amplifier to unbalance the impedance in the flow as between the split paths.

8. In apparatus of the character described, the combination of a split-path hydraulic system, means including a pair of electrically rseponsive transducers each connected to a different one of said paths for impeding the flow of hydraulic fluid in the respective paths at an electrical fre quency, an oscillator for the transducers, a substantially balanced amplifier, the output of which is generally equally supplied to the transducers to create impedance in the flow through said split paths, and adjustable means coupling the output of the oscillator to the amplifier and adjustable to modulate said output unequally for thereby unbalancing the output of said amplifier to unbalance the impedance in the flow as between the split paths.

9. In apparatus of the character described, a hydraulic system having a passage for the circulation of fluid therethrough, and in combination therewith an electrical system comprising an electrically responsive device connected to said passage for impeding the flow of fluid therethrough, and controlled input power delivery means for applying power to operate said electrically responsive device for varying the impedance in said flow whilst the latter continues through said passage.

10. In a device which controls flow by a minute change in the transverse dimensions of the device, a fluid conduit of fixed length and containing within its length a transducer, said transducer having a body of hollow-block material selected from the class consisting of piezoelectric and magnetostrictive materials and formed with a nozzleshaped interior, said body changing primarily in the transverse dimensions of its interior when power energizes said transducer, and means for conducting power to said transducer.

11. In a flow-carrying device which controls flow by repetitive minute changes in the transverse dimensions of the device, a transducer having a body of hollow-block material selected from the class consisting of piezoelectric and magnetostn'ctive materials, and provided with a flow tube in the interior which is gripped by the transducer body and through which a fluid stream is adapted to flow, said transducer changing primarily in its transverse dimensions when power energizes said transducer, and means for conducting power to said transducer causing it to change the transverse dimensions of the tube gripped thereby.

12. In a flow-carrying device which controls flow by a repetitive, minute change in the transverse dimensions of the device, a transducer having a body of a hollowblock of material selected from the class consisting of piezoelectric and magnetostrictive materials, and provided with a thin flow-tube of comparatively small cross section and being of a fixed, substantial length and restriction-free, said hollow-block intimately gripping a portion of the flow tube and changing primarily in its transverse dimension when power energizes the transducer, the interior of said block where it grips the flow tube causing a corresponding change of transverse dimension of said flow tube to create a turbulence of flow in the contents present in the flow tube.

13. In a flow-controlling device of the character described, a transducer unit having a piezoelectric body element with a hollow core, said body element being vibratable primarily transversely with respect to the axis of the core, and means forming respective sleeve and core liner electrodes one within another and with the transducer body aflixed therebetween whereby potential on the electrodes causes the body element to vary in the transverse dimensions of the hollow core.

14. In a flow-controlling device of the character described, a piezoelectric transducer body which is cored on the inside and is vibratable primarily transversely to the axis of the core, a layer of foil on the outside of the body, a fired metallic film on the inside, and means for impressing a potential difference on said foil and film causing the core of the body to vary in its transverse dimensions.

15. The method of utilizing a permanently open restriction and utilizing transverse disturbances in a fluid for controlling the rate of flow of the fluid, comprising the steps of directing the fluid to the restriction, generating waves of energy at a transverse location remote to said fluid and traveling at the speed of sound, and directing said waves of energy through a sonic medium so as to focus at and create transverse disturbances at a point in said fluid prior to departure from said restriction, thereby transversely agitating the flow lines of said fluid for offering increased resistance of flow in passing through said restriction.

16. Method for retarding flow of fluid in a permanently open if not altogether obstruction-free tubular passage of fixed length, comprising the steps of directing the fluid along the inside wall of the tubular passage, and vibrating the tubular passage from its outside wall so as to change primarily the transverse dimensions of the tubular passage, thereby physically creating crosswise disturbances in the fluid immediately in contact with the inside wall to produce turbulence and increased resistance to flow.

17. Method for retarding flow of a fluid in a tubular passage having an axially aligned transducer element in the path of flow, said transducer defining an axial opening of relatively restricted size and being vibratable to change in its physical proportions primarily in the size of the opening, said method comprising the steps of directing the fluid along the inside wall of the opening, and, by application of power to vibrate the transducer, repetitively changing the size of the opening thereby creating crosswise disturbances in the fluid contacting the inside wall of the opening to produce turbulence and increased resistance to flow.

18. In electrohydraulic apparatus of the character described, the combination of an hydraulic system having a passage of fixed length for the circulation of fluid therethrough, and including a permanently open restriction in said passage, means comprising an electrically responsive transducer connected to said passage creating vibrations primarily causing the transverse dimensions of a portion of the passage to change size, thereby impeding the flow of fluid through said restriction therein, and controlled input power delivery means for applying power to operate said electrically responsive transducer for varying the impedance in said flow whilst the latter continues through the restriction in said passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,287,950 Tibbetts June 30, 1942 2,453,595 Rosenthal Nov. 9, 1948 2,509,913 Espenschied May 30, 1950 2,510,811 Gale June 6, 1950 2,895,062 Abbott July 14, 1959. 2,900,536 Palo Aug. 18, 1959 2,915,077 Wehrli et a1. Dec. 1, 1959 2,928,409 Johnson et a]. Mar. 15, 1960 

